1. Field of the Invention
The present invention relates to a radio paging receiver and method for receiving and decoding a non-standard radio paging signal having reduced preamble data.
2. Description of the Related Art
A radio paging receiver (pager) receives and analyzes radio paging information of a specific format. Upon detecting a unique self-identification code from an incoming page, the pager generates an alert tone and displays the paging information.
FIG. 1 is a block diagram of circuitry within a conventional paging receiver that receives paging information called a POCSAG code. According to the CCIR standard, the POCSAG code is comprised of a 576-bit preamble and a plurality of batches. The preamble is a reversible code having a binary "1" and "0" repeated during 576 bits. One POCSAG code usually includes between 30 and 60 batches. Each batch consists of a 32-bit word synchronization code and eight frames of 64 bits each. A radio frequency (RF) receiver 110 receives an RF signal in a POCSAG format through antenna AT. RF receiver 110 frequency-converts, demodulates and shapes the waveform of the received RF signal. A decoder 120 decodes the resulting signal RX output by receiver 110 and sets an operating mode of the pager based on the decoded information. More particularly, during an idle mode, decoder 120 generates a time-varying battery saving signal BSAV which controls a switch 140 coupled between a battery 130 and RF receiver 110, to thereby control operating power supplied to receiver 110. In the idle mode, battery power is saved as switch 140 is periodically opened and closed in accordance with the BSAV signal. When switch 140 is closed in the idle mode, the pager detects incoming preamble data. During a batch mode, decoder 120 detects word synchronization data and frame data, and decodes the detected frame data into its original form.
The battery saving signal BSAV satisfies the CCIR standard. Since, in accordance with this standard, the preamble data contains at least 576 bits, the BSAV signal typically has an OFF period of 512 bits and an ON period of 48 bits. If a preamble data signal containing less than 500 bits is transmitted, which does not satisfy the CCIR standard, the paging receiver does not normally decode it. This phenomenon can frequently happen in a radio paging system with an incomplete configuration. Therefore, for radio pagers operating within such a radio paging system, call success rates are dramatically reduced.